a. Field of the Invention
The present invention is directed to optical techniques for non-invasively performing three-dimensional characterization of ultrasound beams. In particular, the present invention is directed to optical techniques for characterizing high power acoustic beams and fields, including with respect to their non-linearities.
b. Background Art
High power acoustic fields, such as are employed in the practice of medical High Intensity Focused Ultrasound (HIFU) therapy or surgery, are very difficult to measure, as their extreme intensities damage measurement instrumentation. Furthermore, propagation nonlinearities are frequently present, if not dominating.
Thus, existing HIFU transducers are typically tested in a low peak power, and thereby linear, regime (typically from about 1 W to about 3 W, or, in terms of power density, from about 0.01 W/cm2 to about 100 W/cm2) in order to avoid destruction of the measurement apparatus. Manufacturers and developers infer high power behavior (typically, between about 100 W and about 200 W, or, in terms of power density, between about 1500 W/cm2 and about 3000 W/cm2) from the low power test results.
This testing methodology is far from optimal, however, as some of the effect of HIFU is attributable to naturally occurring non-linear high-power phenomena. Consequently, the field of HIFU devices finds itself in the position of lacking metrics related to non-linear operational phenomena.